1. Field of the Invention
The present invention relates to a totally opened F value information input system of the lens for a camera with interchangeable lenses, more particularly to a totally opened F value information input system of the lens by means of which system the totally opened F value information of the photographic lens is put in the digital exposure operation circuit at the side of the camera body as digital information.
2. Description of the Prior Art
When the totally opened F value (totally opened aperture value) of the photographic lens to be used is varied in the case of a camera with interchangeable lenses, presenting the so called TTL exposure control system by means of which the light beam coming from the object to be photographed through the lens is measured so as to determine the exposure value,
(1) THE ABSOLUTE INCIDENT LIGHT AMOUNT FOR THE LIGHT MEASURING ELEMENT FOR MEASURING THE BRIGHTNESS OF THE OBJECT TO BE PHOTOGRAPHED VARIES IN ACCORDANCE WITH THE TOTALLY OPENED F value of the photographic lens to be used, whereby the light measuring element is included in the above mentioned TTL exposure control system and provided at a suitable position in the camera body at which the light beam coming from the object to be photographed through the photographic lens can be received, and
(2) DUE TO THE DIFFERENT POSITION OF THE LIGHT EMITTING PUPILS OF THE INTERCHANGEABLE LENSES AND OTHERS, THE DIFFERENCE OF THE LIGHT AMOUNT ON THE LIGHT RECEIVING PLANE OF THE LIGHT RECEIVING ELEMENT AMONG THE INTERCHANGEABLE LENSES DO NOT CORRESPOND TO THAT ON THE FOCUS PLANE (FILM PLANE) ANY MORE;
In such a manner that the light measurement state varies, whereby, in order to always obtain a sure and accurate operation of the exposure control system, it is essential to compensate the operation by giving the totally opened F value information of the photographic lens to be used to the exposure control system.
Until now the so called analogue amount transmitting method has been adopted for this purpose, whereby the totally opened F value of the interchangeable lens in question is indicated by the length of the signal pin in such a manner that, at the time of mounting the photographic lens on the camera body, a proper compensating device is operated in accordance with the projecting length of this signal pin so that the totally opened F value information of the photographic lens to be used is given to the exposure control system.
In the case of such method, it is necessary to strictly determine the size of each signal pin in accordance with the totally opened F value for the interchangeable lens. However, during the actual production as well as the actual mounting of this signal pin, there takes place a comparatively large error in its size. Since there is provided the above mentioned compensating device between this signal pin and the exposure control system, errors are apt to take place between them so that by means of such analogue amount transmitting method as mentioned above, it is difficult to put a precise totally opened F value information to the exposure control system, which is disadvantageous.
Quite recently, digital techniques have been introduced in the camera and it has been proposed to carry out the operation of the exposure, the indication of the determined exposure value (diaphragm value as well as shutter speed) or the control of the exposure device (diaphragm device or shutter device) and so on by means of digital circuits. Thus, it is necessary to convert the information transmitted as an analogue amount into the digital information. Hereby again errors occur.
In order to eliminate such inconveniences as mentioned above, U.S. Pat. No. 3,782,261 proposes "Data Transmission Device for Use with Interchangeable-Lens-Camera" which is so constructed that on an annular surface of the mount for the lens at the side of the camera body is provided a uniform circular array of data transmission elements, each of which is biased toward a projected position in which it sticks out of the camera mount annular surface, but can be pushed into a retracted position. On a corresponding annular surface of the mount at the side of the interchangeable lens are provided one or more arcuate slots adapted to receive loosely selected data transmission elements when the lens is mounted in its final position on the camera in such a manner that at the time of mounting the lens on the camera selected transmission elements are received in the slot or slots and thus remain in their projected position. Other data transmission elements are pushed into their retracted position by the annular surface of the lens mount so that the data to be transmitted from the lens to the camera is determined by the particular combination of retracted and projected data transmission element in a digital way.
The data transmission device proposed by the U.S. Pat. No. 3,782,261 is especially intended to the interchangeable lenses and the camera of the screw mount connecting system (by means of which system at the time of mounting the interchangeable lens on the camera body the lens is crewed in so as to be connected with the camera body and which system is distinguished from the bayonet mount connecting system) so that the uniform circular array of data transmission elements is combined with one or more slots as explained above whereby for the positioning of each data transmission elements on the annular surface of the camera mount as well as for determining the position of the arcuate slots on the annular surface of the lens mount and the form of the arcuate slots, a strict accuracy is requested and in consequence the accuracy at the time of the data transmission largely depends upon the positioning accuracy of the data transmission elements as well as the positioning and the size accuracy of the arcuate slots. This is done that at times the accurate and sure transmission of data can not be guaranteed, In addition, for the arrangement of data transmission elements as well as the working of the arcuate slots, sophisticated techniques are demanded so that the cost of the data transmission device as a whole goes up, which is not profitable.